Preparation of oximes



United StatesPatent O PREPARATION OF OXIIVIES Sjoerd Kaarsemaker, 'Sittard, Netherlands, assignor to Stamicarbon N. V., Sittard, Netherlands No Drawing. Application September 3, 1953, Serial No. 378,432

Claims priority, application Netherlands September 17, 1952 3 Claims. (Cl. 260-566) The present invention relates to the preparation of oximes by the reduction of primary or secondary nitrocompounds of aliphatic or cycloaliphatic hydrocarbons with hydrogen in the presence of a catalyst.

I-leretofore, the reduction of these nitro-compounds to oximes has been carried out in the liquid phase with reducing agents, such as stannous chloride, in hydrochloric acid solution. Thus, for example, nitro-cyclohexane has been reduced in the liquid phase using reduction catalysts and hydrogen to form cyclohexanone oxime.

In carrying out the reduction of nitro-cyclohexane, as referred to above, it is necessary to insure that there is good contact between the nitro compound, and the catalyst and hydrogen. For this reason, the nitro-cyclohexane is often dissolved in a solvent and the reduction carried out under pressure in a reaction vessel wherein the mixture is stirred intensively. Such a process, however, is not particularly suitable for commercial operations in view of the requirements for solvent and pressure equipment. Moreover, there is the further difl iculty that the reduction is not readily controlled and may easily proceed too far thereby producing large amounts of amine instead of the desired oxime.

Accordingly, it is an object of the present invention to produce oximes by a new and improved reduction process which is free from the difiiculties noted above with respect to prior procedures.

Another object is to provide a process wherein objectional high pressure equipment and the use of a solvent are eliminated.

A further object is to produce oximes by easily controlled reduction thereby obtaining a minimum of undesired amine.

Further objects will become apparent from the detailed description given hereinafter. It is understood, however, that the detailed description and the specific examples do not limit the invention but merely indicate the preferred embodiments of the invention since various changes and modifications within the scope of the invention will become apparent to those skilled in the art.

The foregoing objects are accomplished, according to the present invention, by a process which, broadly stated, comprises passing a mixture of hydrogen and a primary or secondary aliphatic or cycloaliphatic nitrohydrocarbon in the vapor phase over a heated reduction catalyst at a temperature between about 90 to 300 C.

The success of the invention is due, to a large extent, to the discovery that reduction of the nitrohydrocarbon in the vapor phase and within the temperature range stated gives a substantial yield of oxime with little, if any, formation of amine. It is essential that a temperature within the range stated be used and it has been found that the amount of nitro-compound reduced increases proportionally as the reaction temperature is increased. However, at higher temperatures within the Patented Oct. 23, 1956 range stated, it has also been noted that there is somewhat of an increase in the amount of amine formed.

While the process of the invention may be carried out at subor super-atmospheric pressures, atmospheric pressure is preferably utilized since this eliminates the necessity of using pressure-tight equipment. If the reduction is carried out at a temperature which is below the boiling point of the nitro-compound, the vaporization of the nitro-compound may be carried out in any convenient way, e. g., by passing a continuous current of the nitrocompound into a heated evaporation chamber While simultaneously introducing hydrogen. By carrying out the evaporation of the nitro-compound at a temperature which is about equal to the temperature at which the reduction is carried out, separate pre-heating equipment for bringing the vapor up to the reaction temperature may be dispensed with.

Vaporization of the nitro-compound, according to the invention, may be promoted by reducing the pressure. Likewise, and as indicated above, the reduction itself may be effected under a reduced pressure of the order of 100 mm. Hg. Elevated pressures, e. g., up to 5 atmospheres may also be used although, as noted, the great advantage of dispensing with pressure equipment is lost in such event.

The ratio of hydrogen to nitro-compound in the gaseous mixture subjected to reduction can be widely varied. Generally speaking, however, the amount of hydrogen will constitute from 50% to 95%, and preferably between to by volume of the gaseous mixture of hydrogen and nitrohydrocarbon. Either pure hydrogen or gaseous mixtures thereof with such other gases as nitrogen or water vapor, may be employed with substantially equal success.

As the reduction catalyst, any of the well-known hydrogenation catalysts, such as the metals of the 8th group of the periodic system, especially nickel, cobalt or iron may be used. Platinum and copper catalysts are likewise suitable as are compound copper catalysts and compound catalysts consisting of metals and metal oxides, such as copper-cadmium, calcium, silver-Zinc and silverchromium catalysts. As illustrative of the latter, there may be mentioned a catalyst containing 10% cuprous oxide and 90% cadmium oxide and a catalyst consisting of a complex compound of the oxides of chromium, zinc, silver and calcium in the atomic ratio Cr:Zn:Ag:Ca=50:40:5:S.

As indicated above, the reduction, according to the invention, must be effected at a temperature between about 90 and 300 C. Howeventhe temperature can be varied anywhere within this range to give satisfactory results and it is usually necessary to determine the optimum temperature for the particular catalyst which is being used.

The rate of passage of the gas mixture over the catalyst can be widely varied and depends upon the nature of the gas mixture, the catalyst, temperature and other reaction conditions. Generally speaking, however, from liters to 10,000 liters of gas per hour per liter catalyst chamber volume and preferably 200500'liters, are passed over the catalyst to give satisfactory yields.

It has been found that extremely favorable results are obtained with zinc oxide as a catalyst. This catalyst is advantageous because at a high reaction temperature, e. g., -260" 0, wherein a large amount of the nitrocompound is reduced, substantial yields of oxime are obtained and the formation of undesirable amine is slight.

As will be appreciated, the novel process of this invention makes it possible to obtain aliphatic and cycloaliphatic oximes, which are of importance as starting materials for the preparation of other valuable chemical products, in a straightforward manner using relatively simple apparatus. Examples of nitro-compounds which may be reduced and form oximes in this manner are: nitro-ethane, secondary intro-propane, nitro-cyclohexane, methyl nitro-cyclohexane and nitro-cycloheptane.

The process according to the invention is especially important in the reduction of nitro-cyclohexane, from which the cyclohexane oxime is obtained. This material after being converted into caprolactam, is used on a large scale as a raw material for the preparation of polymerization products especially in the synthetic fiber industry.

The following examples illustrate, but do not limit, the present invention.

Example 1 A zinc oxide catalyst was prepared by heating zinc carbonate at a temperature of about 400 C. The reaction product, zinc oxide, was compressed into tablets with a diameter of 3 mm. A reaction column was filled with this catalyst and was heated to a temperature of 250 C. by employing a heating jacket.

In an evaporating chamber hydrogen was passed at a temperature of about 200 C. through a continuous current of nitro-cyclohexane, as a result of which a gas mixture consisting of nitro-cyclohexane vapor and hydrogen was obtained. By adding hydrogen the nitro-cyclohexane content of the gas mixture was adjusted to 13-14% by volume. Subsequently the gas mixture was preheated to v the reaction temperature and passed through the reaction column filled with the catalyst, whilethe temperature was maintained at 250 C. during the reduction. The rate at which the gas mixture was passed through the catalyst chamber was 350 liters per hour per liter of catalyst chamber volume. The reduction was carried out at atmospheric pressure. The gas mixture leaving the reaction chamber was introduced into a condensation chamber, in which a mixture of non-converted nitro-cyclohexane and the cyclohexanone oxime formed was condensed and separated from the residual gas. In this manner 73% of the nitrocyclohexane appeared to have been converted, of which 76% was converted into cyclohexanone oxime and only 4.5% into cyclohexyl amine.

By cooling down the condensed reaction product to below C. the oxime is separated off in the crystalline form, in which process about 10% of the oxime remains in solution at about room temperature. The liquid separated from the crystals after removing the water and amine contained therein by distillation at a temperature of from 130 to 140 C., may be returned to the evaporation chamber. The reduction carried out in this manner is a continuous process. It is not hindered by the presence of a small quantity of oxime in the recycled nitro-cyclohexane and the amount of amine formed is not increased to any extent by this amount of oxime.

Example 2 In the manner described in Example 1, a gas mixture containingrfrom 14-15% by volume of nitro-cyclohexane vapor was obtained by the evaporation of nitro-cyclohexane with hydrogen. This mixture was introduced into the reaction chamber at the rate of 350 liters per hour per liter of catalyst chamber volume. The reduction was carried out at 190 C. at atmospheric pressure.

12% of the nitro-cyclohexane appeared to have been converted of which amount 97% was converted into cyclohexanone oxime and on1y2% into cyclohexyl amine.

Example 3 A catalyst consisting of a complex compound of the oxides of chromium, zinc, silver and calcium, in the atomic ratio Cr:Zn:Ag:Ca=:40:5:5, was prepared by adding an aqueous solution of zinc nitrate, silver nitrate and calcium nitrate to a warm ammonium bichromate solution and heating the resulting precipitate to about 400 C. The product obtained in this manner was compressed into tablets with a diameter of 3 mm. and this catalyst was used for the reduction according to the process of Example 1.

A mixture of nitro-cyclohexane vapor (5% by volume), hydrogen (20% by volume) and nitrogen by volume) was prepared by evaporating nitro-cyclohexane at 103105 C. while passing a mixture of nitrogen and hydrogen through it.

This gas mixture was passed through the catalyst chamber at the rate of 2500 liters per hour per liter of catalyst chamber volume. The reduction was carried out at a temperature of from 103 to 105 C. at atmospheric pressure.

In this manner 10% of the nitro-cyclohexane was converted, 94% by weight of which amount was converted into cyclohexanone oxime and 6% into cyclohexyl amine.

As will be appreciated, various modifications of the invention as described herein can be made without deviating from the scope thereof. Hence, it will be appreciated that the invention is not limited by the foregoing description and should be construed according to the appended claims wherein I claim:

1. A process for the production of cyclo-hexanone oxime which comprises the steps of forming a gaseous mixture of hydrogen and nitro-cyclohexane by passing hydrogen through a continuous current of said nitro-cyclohexane and adjusting the contents of the resulting gaseous mixture so that the nitro-cyclohexane content is 1314% by volume, preheating the gaseous mixture to a reaction temperature within the range of to 300 C., and passing said preheated mixture at atmospheric pressure over a zinc oxide catalyst while maintaining same at reaction temperature.

2. The process of claim 1 wherein the rate of passage of said gaseous mixture over said catalyst is to 10,000 liters per hour per liter of catalyst.

3. A process for the production of cyclo-hexanone oxime which comprises passing a mixture by hydrogen and nitrocyclohexane in the vapor phase and at atmospheric pressure over a zinc oxide catalyst at a temperature of between and 260 C.

References Cited in the file of this patent 

3. A PROCESS FOR THE PRODUCTION OF CYCLO-HEXANONE OXIME WHICH COMPRISES PASSING A MIXTURE BY HYDROGEN AND NITROCYCLOHEXANE IN THE VAPOR PHASE AND AT ATMOSPHERIC PRESSURE OVER A ZINC OXIDE CATALYST AT A TEMPERATURE OF BETWEEN 185* AND 260* C. 